Suture needles are often colored to assist a surgeon in visibly distinguishing the needle and visually locating the needle point in the surgical field in which the surgeon is performing a surgery. For example, if the surgical field is filled with fluid it may be difficult for the surgeon to see a silver colored needle against the fluid, or against tissue that is surrounded by fluid such as saline or blood. Moreover, the bright lights commonly used in surgery strongly reflect from silver needles, producing a glare that compounds the difficulty of seeing the point of the surgical needle. Additionally, certain surgeries, particularly coronary artery bypass surgery, necessarily involve the use of suture needles of small diameter, which are difficult to visually distinguish in the surgical field due to their small size. In response to the need to visibly distinguish the suture needle from the surgical field, stainless steel needles have been colored black using coloration processes that may require toxic chrome bearing solutions. In addition to the special handling procedures that must be implemented when using these chrome bearing solutions, they also pose an environmental hazard and considerable care must be taken in their disposal.
When utilizing suture needles having small diameters, it is desirable for such needles to have exceedingly high bending stiffness and strength. In particular, surgery of this type requires that the path of the suture needle be closely controlled. If the needle flexes excessively as it enters the tissue or as it pierces the inner surface of a blood vessel before re-emerging, improper placement of the needle and serious trauma to the tissue and the patient may possibly occur. In use, suture needles may be subjected to significant stressing forces to overcome frictional drag through the tissue. These forces resisting needle penetration often occur in patients undergoing cardiovascular surgery who exhibit calcified or toughened tissue due to coronary artery disease. In these procedures, the suture needle must be able to pass through not only the blood vessel, but also any hard calcified tissue that may be located along the periphery of the blood vessel lumen. An overly compliant needle may deflect elastically during tissue penetration and may result in a loss of placement control. As such, it is preferable that the needle should have a relatively high bending stiffness, that is, a low tendency to flex and high tendency to retain its configuration when subjected to a deforming force. Hence, stiffness in bending is a desirable property for the handling and performance of suture needles. A stiff needle resists elastic deflection and can thus be directed as intended to provide a high level of control.
Thus, there is a need for suture needles that exhibit high robust surface coloration, particularly for surgical procedures that require small diameter needles.